1. Field of the Invention
The present invention relates to a fuel supply apparatus and a fuel supply control apparatus for an internal-combustion engine.
2. Description of Related Art
Reduction in environment pollution caused by exhaust gas, and a response to resource depletion are formidable challenges to a current transportation system led by automobiles. Development of alternative fuel to conventional hydrocarbon fuel, and improvement of gasoline and light oil fuel are under consideration as alternative fuels to automotive fuel. The improved gasoline and light oil fuel can be employed in an existing engine without modification, which is advantageous on the cost front. For example, mixed fuel as a result of mixing inexpensive alcohol into gasoline, and fuel as a result of reducing aromatic components in gasoline are known.
However, mixed fuel including alcohol has poor ignition performance as compared to gasoline fuel, thereby deteriorating starting performance at low temperature or in a cold region. Furthermore, since alcohol is more easily vaporized than gasoline fuel, alcohol is vaporized in a fuel flow passage in an injection valve at the high-temperature restarting, so that a vapor lock may be caused.
In a conventional fuel supply device for alcohol mixed fuel according to JP61-11445A, a high molecular membrane for separating an alcohol component is provided in a fuel tank to store separately fuel having high concentration of alcohol and fuel having low concentration of alcohol, and there are two systems of fuel supply passages from two respective storage portions to an engine. The two systems of fuel supply passages are connected to a fuel passage leading to an injector via respective pumps. A change-over valve supplies or stops supplying fuel having high concentration of alcohol, so that fuel is supplied according to an operational condition of the engine.
In a fuel storage device for an engine according to JP5-209565A, a tank for alcohol-containing fuel and a tank for gasoline fuel are separately provided to selectively use alcohol-containing fuel or gasoline fuel according to an operational condition of the engine, without providing a separation membrane. In the fuel storage device, a fuel tank is divided between a first tank for gasoline fuel and a second tank for alcohol-containing fuel, and the first and second tanks are connected to a fuel pump through respective valves. Accordingly, fuel to be supplied to an injector from the fuel pump through a fuel supply pipe can be selected. In addition, an oil feeding detecting means and an alcohol concentration detecting means are provided, to prevent wrong fuel feeding.
Since gasoline fuel includes various kinds of components (e.g., paraffinic, olefinic, and aromatic), a part of the components cannot be vaporized at cold starting and is sometimes discharged without complete combustion. To combat this, a fuel supply unit having an aromatic component reduction device for reducing aromatic components in fuel is disclosed in JP2004-19614A. The fuel supply unit includes a tank, in which aromatic component reduced fuel is stored, and a means for circulating the aromatic components absorbed in the aromatic component reduction device to a fuel tank, to supply aromatic component reduced fuel in a warm-up process at starting of an engine, thereby reducing hydrocarbon in exhaust gas.
However, the device in JP61-11445A requires the two systems of fuel supply passages and pumps, which results in its complex configuration. Besides, the respective fuel supply passages join to be the fuel passage leading to the injector. Accordingly, even if the supply of alcohol fuel is stopped at the starting, a substantial amount of fuel having high concentration of alcohol, which is supplied before then, is left in a fuel pipe or a delivery pipe. As a result, fuel with its alcohol component separated cannot be promptly injected from the injector, and thereby a sufficient improvement effect on starting performance is not produced.
In the device disclosed in JP5-209565A as well, because alcohol-containing fuel and gasoline fuel flow through the same fuel passage on a downstream side of the fuel pump, prompt switching between fuels is not carried out, so that similar problems are caused. Furthermore, since the tank for alcohol-containing fuel and the tank for gasoline fuel are separately provided, it takes man-hours to feed fuel to each of the tanks, and an oil feeding time control means is needed to prevent wrong fuel feeding.
In the unit disclosed in JP2004-19614A, the aromatic component reduction device and the aromatic component reduced fuel tank, which is on a downstream side of the aromatic component reduction device, are provided independently of the fuel tank, so that the unit tends to grow in size. Moreover, since each tank is connected to a passage inside an engine through a fuel pipe, fuel is left in a delivery pipe, so that similar problems about starting performance are caused.